The Doctor immediately begins investigating his old friend's problem. He uses his heightened olfactory senses to determine that something about the milk in his tea is "off". Lloyd's human senses aren't keen enough to detect anything, so the Doctor is forced to prove it through careful examination of the milk. He discovers a fungus that he enigmatically says that he's seen before. When asked why the milk isn't affecting other animals, like humans, the Doctor surmises that cats are simply particularly susceptible.

The time traveller then begins to question Lloyd about the current origin of Britain's milk. The Time Lord is surprised to discover that the tanks in which the milk is being stored comes from Houston, Texas. Somehow, the fungus has spread from outer space to the Houston-made milk vats to the cats of Britain.

The Doctor uses his previous knowledge of the fungus to develop a quick solution: a high-pitched sound, as delivered from a dog whistle, will successfully knock out the virus. He leaves it in Lloyd's hands to get the government of Britain to co-ordinate short bursts of sound from radio stations around the country.

The story features a trope that was extraordinarily common in World Distributors' annuals: that of the Doctor meeting an "old friend" of whom the readers were not previously aware. The trope allowed the writer to get away with depicting a close relationship with the Doctor without having to explain why. This shorthand was extremely valuable to World Distributors authors, given the brevity of the stories.